The Occupational Studies Section (OSS), Environmental Epidemiology Branch (EEB), Epidemiology & Biostatistics Program (EBP), Division of Cancer Etiology (DCE), National Cancer Institute (NCI) and the National Institute for Occupational Safety and Health (NIOSH) are collaborating to develop a user friendly, flexible, computerized system for documentation of descriptive data and for development of quantitative estimates of occupational cohort studies. The purpose of this contract is to convert the computerized exposure assessment system developed for the acrylonitrile study into a more user friendly, flexible, system for documentation of descriptive data and for development of quantitative estimates of occupational cohort studies. The requirements of the system would be that it be adaptable to a wide variety of epidemiologic investigations and that it incorporate both quantitative and qualitative information on exposures. The estimation methods would incorporate a few standardized algorithms, but would be designed to allow users to develop their own estimation procedures.